Ye. The advantage is that when all your ship's command centers are destroyed, your ship blows up and you die. The selection of which internal components are destroyed in any given hit is completely random. Therefore if you have more command centers, your ship is less likely to get blown up unexpectedly in a single shot. More command centers don't do much to improve your combat abilities. In fact they can actually reduce your combat abilities slightly by using up space and credits which could otherwise be used for other components such as stealth and radar units which would improve your combat abilities much more. However, more command centers do dramatically improve your commander's survival rate if you don't have many shields on your ship, because they lessen the likelihood of your ship being blown up from a sudden hit.

Just to add to what CMGeek said, it's worth remembering that command centers can be fixed by repair bots, whereas shields cannot - so to some extent, you can use them like rechargeable, omnidirectional shields (although they can absorb far less damage, and do not protect other components the way shields do).

For very cheap ships, multiple command centres are generally more effective than shields, as they eliminate the risk of being killed by a single lucky shot (it's always worth having at least 1 front shield though). For more expensive ships, shields are generally more effective, because they absorb more damage and don't take up component slots.
Early in the game, stealth units are the best defense of all (so much so that using them feels like cheating), but they lose their effectiveness later in the game, when you're always surrounded by large numbers of enemy ships.